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What is cholesterol and why are there "good" and "bad" varieties?

Cholesterol is an important constituent of body cells. This lipid, or fatty substance, is produced mostly in the liver. It is involved in the formation of bile salt (salt produced in the liver) and hormones, and in the transport of fats in the bloodstream to the tissues throughout the body. Cholesterol and fats are packaged together with proteins, in substances called lipoproteins.

High cholesterol levels in the blood may lead to a narrowing of the inner lining of the coronary (heart) arteries. (Arteries are any of the elastic-walled blood vessels that carry blood from the heart to other parts of the body.) This increases the risk of heart disease or stroke. (A stroke is a sudden loss of brain function caused by a blockage or rupture of a blood vessel to the brain.) An overabundance of cholesterol in the bloodstream can be an...

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